This invention relates to a method and apparatus for in-vivo, real time measurement of pH, pCO2, base excess, hemoglobin, and hemoglobin oxygen saturation. More particularly, the invention relates to an apparatus placed in-line with an existing invasive patient access line to provide continuous, semi-continuous, or non-continuous monitoring of blood pH, pCO2, base excess, hemoglobin, and hemoglobin oxygen saturation in a manner which is relatively non-invasive. Further, the device and apparatus allows monitoring of the listed parameters in a non-destructive manner such that the blood sample under analysis can be returned to the patient.
Although body fluid analyzers are known in the art, presently available sensors use electrochemical sensors, also known as electrodes to measure blood parameters such as pH and pCO2. See U.S. Pat. Nos. 3,874,850; 4,097,921; 4,579,641; 4,615,340. Such electrode measurement techniques often require a great deal of costly equipment and frequent maintenance. Typically, an elaborate 2-point calibration is required. Acceptable accuracy with reusable electrochemical systems is obtained only with an additional step of cleaning the electrodes with a washing solution after each use. The alternative approach to electrochemical sensors utilized in the method and apparatus described herein is based upon the hydrogel dye film sensing elements described in international publication number WO 90/00572.
The determination of blood pH, pCO2, hemoglobin, and hemoglobin oxygen saturation include in-vivo techniques by which a blood sample is withdrawn from a patient and sent to a laboratory for analysis. This technique has several drawbacks. The blood sampling and transfer to a laboratory requires addition of anti-coagulants or other preservative agents rendering the sample unsuitable for return to the patient. The blood sample tested reflects a single measurement and does not provide any indication of stability or fluctuation over time. Laboratory in-vivo methods do not permit continuous monitoring of blood pH, pCO2, hemoglobin, and hemoglobin oxygen saturation. Means for obtaining a blood sample for study involve invasive techniques and thus pose risks of infection or introduction of emboli to the bloodstream. Frequently, repeated measurements deplete blood volume, particularly of infants and small children, and involve repeated risk exposure. The time elapse between sample withdrawal and analysis delays complete diagnosis and determination of course of treatment for a patient who may be critically ill.
Oximeters have been utilized for in-vivo determinations of blood hemoglobin oxygen saturation, but have not been used to provide information on hemoglobin concentration. Such methods employ xe2x80x9cnaturally occurring cuvettesxe2x80x9d, for example, the earlobe or the finger. Results obtained with these oximeters are often adversely affected by interference from venous blood, tissue, bone, ambient light, or patient motion.
Limitations encountered in some in-vivo oximeters have led to the development of intravascular oximeters. Such devices employ some indwelling components in a vessel and obtain saturation by reflection spectrophotometry.
Spectrophotometric techniques used to determine blood hemoglobin oxygen saturation may be subject to measurement error caused by the presence of dyshemoglobins in the blood sample. Dyshemoglobins, such as methemoglobin and carboxyhemoglobin, cannot transport oxygen but possess spectral absorbance which may interfere with the absorbance of oxyhemoglobin, depending upon the wavelength of the incident light used.
Spectrophotometric measurements of blood hemoglobin oxygen saturation and hemoglobin concentration of non-hemolyzed whole blood are difficult and require sophisticated mathematical models, and cannot achieve clinical accuracy.
It is an object of the present invention to provide an in-vivo, real time measurement of blood pH, pCO2, hemoglobin oxygen saturation by means of an apparatus which is placed in-line with existing invasive patient access lines.
It is a further object of the present invention to provide an apparatus which does not limit access line function, and yet, may be used to provide continuous or non-continuous monitoring of blood pH, pCO2, hemoglobin and hemoglobin oxygen saturation.
It is a further object of the present invention to provide a means of rapidly determining the measurement of blood pH, pCO2, and hemoglobin oxygen saturation in a manner which utilizes a minimal blood volume in such a manner that the blood is not tested destructively, and may be returned to the patient.
And, it is a still yet a further object of the present invention that the sensors and blood chambers utilized in the measuring process be comprised of a sterile disposable cuvette which eliminates the need for cleaning and/or sterilizing of the instrument, and which eliminates the need for frequent calibration of the device.
These and other objects of the invention are realized in a preferred embodiment of the present invention.
The apparatus is comprised of: 1) a disposable cuvette containing blood chambers and sensors for measurement of pH, pCO2, hemoglobin, and hemoglobin oxygen saturation, 2) a readout head containing the means of detecting the signals from the sensors, 3) electronic circuitry for processing and conditioning the electronic signals from the readout head, 4) computer circuitry to analyze the signals and compute the resultant pH, pCO2, hemoglobin, and hemoglobin oxygen saturation, 5) computer software to use in processing the signals, and 6) display means to provide the results to the user.
The present invention also provides a method of determination of hemoglobin and hemoglobin oxygen saturation by means of combining a multi-chambered sampling cuvette with photo-sensors for pH and pCO2, optically diffusing walls and a separate chamber for diffuse transmittance determination of hemoglobin and hemoglobin oxygen saturation, and a subminiature spectrophotometer measurement system with a dual channel transmission/reflectance system for pH and pCO2 measurement, and a further diffuse transmission system for hemoglobin and hemoglobin oxygen saturation measurement. This method and apparatus allows continuous monitoring of the most common blood analyses performed on critically ill patients.
The method provides the measurements without requiring handling of body fluid samples. Further, the method provides the measurements in a rapid fashion without the otherwise wait for laboratory procedures to be accomplished. Further, the method provides the measurements without destruction or contamination of the sample, allowing the sample to be returned to the patient. Further, the method allows repeat measurements with the same sensor without requiring cleaning of the sensor between measurements.